Atmospheric Oxidation of Biogenic Hydrocarbons: Reaction of Ozone with β-Pinene, d-Limonene and trans-Caryophyllene

Several gas-phase carbonyl products of two terpenes, β-pinene and D-limonene, and of the sesquiterpene, trans-caryophyllene, have been identified and their concentrations measured in experiments involving the reaction of these unsaturated biogenic hydrocarbons with ozone in the dark. Cyclohexane was added as a scavenger for the hydroxyl radical to minimize interferences from OH, which forms as a product of the ozone-hydrocarbon reaction. Carbonyl products were formaldehyde (yield = 0.42) and nopinone (yield = 0.22) from β-pinene, formaldehyde (yield = 0.10) and 4-acetyl-1-methylcyclohexene from D-limonene, and formaldehyde (yield 0.08) from trans-caryophyllene. The nature and yields of these products are discussed in terms of the ozone-olefin reaction mechanism. The ozone-β-pinene reaction rate constant, measured in the presence of cyclohexane, is 12.2 ± 1.3 × 10⁻¹⁸ cm³ molecule⁻¹ s⁻¹ at 22 ± 1 °C. Carbonyl products have also been identified in exploratory experiments with trans-caryophyllene and NO in sunlight.